package exercises.leetcode;

import java.util.Deque;
import java.util.LinkedList;

/**
 * <a href="https://leetcode-cn.com/problems/yong-liang-ge-zhan-shi-xian-dui-lie-lcof/">
 * 剑指 Offer 09. 用两个栈实现队列</a>
 *
 * @author or2
 * @Description 用两个栈实现一个队列。队列的声明如下，请实现它的两个函数 appendTail 和 deleteHead ，分别完成在队列尾部插入整数和在队列头部删除整数的功能。(若队列中没有元素，deleteHead 操作返回 -1 )
 * @create 2021年09月19日 时间: 20:38
 */
public class Offer09 {

    /**
     * Your CQueue object will be instantiated and called as such:
     * CQueue obj = new CQueue();
     * obj.appendTail(value);
     * int param_2 = obj.deleteHead();
     */
    private static class CQueue {

        private final Deque<Integer> stackPush;
        private final Deque<Integer> stackPop;

        public CQueue() {
            stackPush = new LinkedList<>();
            stackPop = new LinkedList<>();
        }

        public void appendTail(int value) {
            stackPush.push(value);
        }

        public int deleteHead() {
            if (stackPop.isEmpty()) {
                while (!stackPush.isEmpty()) {
                    stackPop.push(stackPush.pop());
                }
            }
            if (stackPop.isEmpty()) {
                return -1;
            }

            return stackPop.pop();
        }
    }

}
